Shelf



FIG. 1 is a front perspective view of a shelf showing my new design;

FIG. 2 is a front elevation view thereof;

FIG. 3 is a top plan view thereof;

FIG. 4 is a rear elevation view thereof;

FIG. 5 is a bottom plan view thereof; and,

FIG. 6 is a right side view thereof and of which a view taken from the left side would be a mirror image. 

The ornamental design for a shelf, as shown and described. 